Can Community Structure Track Sea-Level Rise? Stress and Competitive Controls in Tidal Wetlands

Climate change impacts, such as accelerated sea-level rise, will affect stress gradients, yet impacts on competition/stress tolerance trade-offs and shifts in distributions are unclear. Ecosystems with strong stress gradients, such as estuaries, allow for space-for-time substitutions of stress factors and can give insight into future climate-related shifts in both resource and nonresource stresses. We tested the stress gradient hypothesis and examined the effect of increased inundation stress and biotic interactions on growth and survival of two congeneric wetland sedges, Schoenoplectus acutus and Schoenoplectus americanus. We simulated sea-level rise across existing marsh elevations and those not currently found to reflect potential future sea-level rise conditions in two tidal wetlands differing in salinity. Plants were grown individually and together at five tidal elevations, the lowest simulating an 80-cm increase in sea level, and harvested to assess differences in biomass after one growing season. Inundation time, salinity, sulfides, and redox potential were measured concurrently. As predicted, increasing inundation reduced biomass of the species commonly found at higher marsh elevations, with little effect on the species found along channel margins. The presence of neighbors reduced total biomass of both species, particularly at the highest elevation; facilitation did not occur at any elevation. Contrary to predictions, we documented the competitive superiority of the stress tolerator under increased inundation, which was not predicted by the stress gradient hypothesis. Multifactor manipulation experiments addressing plant response to accelerated climate change are integral to creating a more realistic, valuable, and needed assessment of potential ecosystem response. Our results point to the important and unpredicted synergies between physical stressors, which are predicted to increase in intensity with climate change, and competitive forces on biomass as stresses increase

Eosinophil and mast cell parameters in children with stable moderate asthma

Mast cells and eosinophils are important cells that contribute to the process of inflammation in asthma either by activating other cells or by secreting products which are potentially toxic to the respiratory epithelium. The influx of these cells in the airways and the secretion of toxic products by these cells is abrogated by inhaled corticosteroids. Methods - In a double blind randomised, placebo controlled, study in children with stable moderate asthma (N = 34, 15 children received fluticasone propionate (FP), an inhaled corticosteroid, and 19 children used a placebo), we investigated the influence of treatment with FP 100 mu g bd on Various parameters of inflammation: number of eosinophils, secretory products of eosinophils i.e. ECP and EDN (in serum and urine) and a secretory product of mast cells, histamine, which is determined as the compound to which histamine is converted and excreted by the human body: NT-methyl-histamine. Results - Previously we reported that lung function increased and bronchial hyperresponsiveness decreased in the 30 children that completed the study during treatment with FP. In these children we found that none of the laboratory parameters of inflammation changed significantly during treatment with either FP or placebo. However, the decrease in urinary EDN almost reached significance (P = 0.07). Conclusions - Our results indicate that the number of eosinophils, serum ECP and EDN and urinary EDN as well as urinary N-T-methyl-histamine do not reflect asthma disease activity in children with stable moderate asthma. Our data on urinary EDN warrant further study of the use of this parameter to monitor asthma in children